The present invention generally relates to industrial baghouses and more particularly to an air filter cartridge for removing particles or dust from a stream of air moving through the baghouse.
Continuous emphasis on environmental quality has resulted in increasingly strenuous regulatory controls on industrial emissions. One-technique which has proven highly effective in controlling air pollution has been separation of undesirable particulate matter from a gas stream by fabric filtration. Such filtration is carried out in dust collection apparatus known in the trade as a xe2x80x9cbaghousexe2x80x9d which operates on the same general principle as an ordinary household vacuum cleaner, except on a much larger scale. Basically, the baghouse is a sheet metal housing divided into two chambers, referred to as plenums, by a tube sheet. Disposed within openings in the tube sheet are fabric filters (also referred to as air filter cartridges). A particulate laden gas stream induced by the action of a fan, blows into one chamber (dirty air plenum) wherein dust accumulates on the fabric filter as the gas passes through the fabric into the other plenum (clean air plenum) and out an exhaust. Although all baghouses are designed in accordance with the foregoing general principles, there are numerous operation and structural distinctions including numerous differences in the structure of the air filter cartridge. The present invention relates to a baghouse wherein a plurality of cylindrical air filter cartridges having closed lower ends are vertically suspended in the dirty air plenum from the tube sheet. The upper ends of the air filter are fixed to openings in the tube sheet. Filtration of the process gas occurs from outside to inside of the filters (i.e., the dust collects on the outside surface of each air filter cartridge).
During continuous operation of the baghouse, the bags must be periodically cleaned and the accumulated dust removed. This may be done by interrupting the flow of the process gas carrying particulate matter and then causing reverse cleaning air to flow from the clean air plenum to the dirty air plenum. The reverse flow of cleaning air causes the dust cake to be dislodged and fall from the exterior of the filter cartridge to the bottom of the dirty air plenum for removal by an auger or similar means. In some baghouse installations, reverse air cleaning may also be supplemented with mechanical shaking of the filters.
Even when a filter bag is properly installed, it is reasonable to expect the fabric to stretch and deteriorate with age and with repeated cycles between the filtering and cleaning modes of operation. Thus, the filters must be periodically checked and replaced.
The installation and maintenance of filter cartridges of this type has traditionally been a time consuming and costly operation. Accordingly, there has been a long felt need in this industry for improvements in filter-cartridge assemblies and mounting techniques to alleviate the many installation and maintenance difficulties which have been encountered.
In the past, a filter cartridge has been proposed (such as in European patent publication number 0 160 168 A2) which comprises a pleated filter medium disposed between an open end cap and a closed end cap. The filter medium is woven through off-set inner and outer support wires which defined the pleated arrangement. The support wires are attached at each end to a frame within the end caps and are formed to exert pressure on the filter medium to support it against inner pressure from a pulsed jet cleaning device.
Additionally, the filter cartridge of the ""168 publication utilizes a separate securing bolt inserted upward through the center of the lower end cap and secured to a threaded recess proximate the upper end cap in order to seal the cartridge to the support frame. Hence, this filter cartridge is quite difficult to install and remove.
An alternative filter cartridge has been proposed, such as in World Patent 90/11116, which attempts to minimize the amount of filtered material which passes through the filter when the pleated filter material is torn. The filter of the ""116 patent discloses a pleated filter, each fold of which defines a longitudinally extending triangular pocket. A filter pipe is inserted along the interior of the pleats and constructed with continuous longitudinal ridges along a length thereof. The ridges form rib shaped elements extending along the longitudinal axis of the filter and having a triangular cross section substantially corresponding to that of the pockets formed about the interior contour of the pleats. The ridges may consist of a foam material applied to the filter pipe.
The filter cartridge of the ""116 patent may be attached to a metal retaining plate through a retaining lip formed at the filter""s upper end. The retaining lip includes an external annular grove about its perimeter which receives the retaining plate in order to hold the cartridge in position. The pleat pack is suspended from the retaining lip. An interior annular groove is provided proximate the external annular groove. The interior groove receives an expanding part having an expanding ridge about its perimeter. The expanding part is securely mounted to the filter pipe which is suspended therefrom. The expanding part and the retaining lip are formed as separate components. To install the filter cartridge into the support frame, the expanding part and filter pipe are removed from the retaining lip to allow the retaining lip to compress inward and pass through an opening in the lower end of the retaining plate. Once the retaining plate is received within the outer notch of the retaining lip, the expanding part is inserted upward through the pleat pack with the filter pipe oriented such that the pipe folds aligning with the ridges about the pleat.
An alternative filter cartridge has been proposed, in European patent (EP 0 498 757 A1), which is intended to prevent build up of dirt particles about the bottom end of the filter cartridge. To achieve this objective, the cartridge of the ""757 patent forms a lower end cap which substantially follows the star shaped pattern of the pleats. The filter cartridge of the ""757 patent is manufactured by placing the filter star tightly upon a base plate. A liquid compound, which when hardened will form the bottom end cap, is applied to the sealed base plate, within the filter star. The liquid material flows into the inner recesses in the filter star to fill the inner radial folds of the star-shaped pleats.
However, the systems proposed heretofore have experienced disadvantages. In particular, the filter cartridges of the ""116 patent and ""168 publication require unduly complex structures having multiple parts which must be assembled before the cartridges are inserted. Such assembly is extremely difficult. Further, the filter cartridge of the ""168 publication utilizes a bottom end cap which bridged the spaces between adjoining pleats within the filter medium, thereby forming a ledge about the bottom of the filter cartridge. This ledge collects dust and filtered material which clogs the lower end of the filter cartridge.
The cartridge of the ""116 patent utilizes an inner cage having triangular shaped ridges extending longitudinally there along about its perimeter. To insert this cage, and the expanding part on the top end thereof, each of the triangular ridges must be aligned with a corresponding triangular recess in the perimeter of the pleats. This alignment is extremely difficult. Moreover, to remove the filter cartridge of the ""116 patent, the retaining part and the cage must first be removed before the pleats can be removed. This operation undesirably complicates the filter changing process.
The cartridge of the ""757 patent requires an overly complex manufacturing process. Additionally, the filter of the ""757 patent utilizes an inner cage within the filter element which is permanently secured to rigid top and bottom end caps. Hence, the filter of the ""757 patent exhibits an extremely rigid structure encompassing both end caps, thereby requiring separate securing means to attach the filter to the system. The separate securing means increase the number of parts and necessitate unduly complex installation and removal processes.
It is an object of the present invention to overcome the problems experienced by the foregoing systems.
More particularly, an object of the invention is to provide a pleat pack filter cartridge of a unitary construction for installation in the tube sheet of a baghouse. Opposite ends of the pleat pack are integrally received within a bottom end cap and an upper fitting. The bottom end cap may be molded to follow the contour of the pleat pack, or may be molded as a disk with an inwardly projecting groove to centrally align the pleat pack therein. The upper fitting is formed of a resiliently flexible material and includes an upper flange to overlie and seal with the upper surface of the tube sheet, a tube sheet mouth insert to seal with a circular opening in the tube sheet, a contoured transition to seal with the lower surface of the tube sheet, and a lower cylindrical collar which permanently secures the upper end of the filter. The contoured transition of the fitting is alternatively molded with either an exterior bulge or an interior bulge. The transition with an exterior bulge is resiliently deformed inwardly to pass through the circular opening of the tube sheet during installation. The transition with an interior bulge freely passes through the circular opening of the tube sheet during installation and then receives an expander to outwardly deform the material to seal with the lower surface of the tube sheet. The upper flange of the fitting may be formed as circumferential scallop edge to facilitate tool access for removal of the expander.